Over at Salon, there's a great article by Peter Finocchiaro about all those mysterious billboards and ads online about how the world is going to end on May 21 - a week from tomorrow. Apparently, they're the work of a splinter group of Christians who follow Harold Camping. Though decades ago Camping incorrectly identified 1994 as the year that the world would end, that hasn't deterred him or his followers. They are convinced now that May 21 is the day. Here's Camping's evidence, as summed up by Finocchiaro:

It's the anniversary of Noah's Flood: A great deal of effort has been made by biblical literalists over the years to identify the exact chronology of the events dictated in the Old Testament. Some scholars, including Camping, adhere to the theory that the Biblical Flood took place on May 21 in the year 4,990 B.C. Then, in Genesis, God told Noah seven days before the Flood to warn people of the impending cataclysm. And Camping posits that this figure, seven days, holds greater significance than meets the eye. According to the biblical passage 2 Peter 3:8, "one day is with the Lord as a thousand years, and a thousand years as one day." Therefore, argues Camping, Rapture should occur 7,000 years after the Flood. And the 7,000th anniversary of the biblical deluge, by his math, falls on May 21, 2011.

It's the anniversary of Creation ... sort of: Another piece of evidence — explained by Family Radio affiliate eBibleFellowship — suggests that the world began in 11,013 B.C., and its 13,000th anniversary came and went in 1988. During that year, apparently on May 21, the end of the "church age" came to pass. Then, a 23-year time of "tribulation" began, during which Satan claimed dominion over all the world's churches. (Camping also supports this notion. He claims that the number "23" — far from just being a poorly received Jim Carrey film — also represents "destruction" in biblical symbology.) The end of this particular period of cosmological strife is said to fall on May 21, 2011.

Divine Numerology: This elaborate line of reasoning first argues that Jesus Christ was killed on April 1 in the year 33 A.D. Using that date, the crucifixion would have occurred exactly 1,978 years and 51 days — or 722,500 days — before May 21, 2011. It turns out that 722,500 is also the product of an equation — (5 x 10 x 17)^2 — that includes three different numbers of significance, according to Camping. Five means "atonement." Ten indicates "completeness."And 17 signifies "heaven." Thus: Armageddon.